They didn't build it from "nothing." The UFC was already fully formed and functional when they "bought" it from Bob Meyrowitz' SEG. SEG only sold to the Frittatas because they couldn't get event permits to generate money. Remember, there was a fight for legalization of this sport due to it being perceived as "human cockfighting" by some. In fact, if Lorenzo hadn't denied the UFC event permits when he was head of the NSAC, SEG might have never sold to the Frittatas at all....
This is the correct answer.
No. Not just anyone can start a casino. They are their own special license to print money off of the rubes. Heck, even Lorenzo and Frank's father was banned from the casino because of his involvement in the money skim which was portrayed in the movie, "Casino." Those guys were "affiliated," if you know what I mean. Also, running the UFC is a pain in the ass because it is such a specialized, niche, sport, and because it relies on people from questionable social and financial status being coerced by social and economic pressures to participate. This is why so many fighters walk away when they get a taste of real money. They are better off with the casinos, which are easier to run.
You are correct. They tried to buy the Raiders. They have a private venture fund that invests their money.